Electrically heated furnace for molten metal



Dec. 20, 1966 H. J. PROFITT ETAL 3,293,412

ELEGTRICALLY HEATED FURNACE FOR MOLTEN METAL Filed May 14, 1964 United States Patent 6) 3,293,412 ELECTRICALLY HEATED FURNACE FOR MOLTEN METAL Henry Joseph Profitt, Evesham, and David Walter King, Solihull, England, assignors to Morganite Thermal Designs Limited, Norton, England Filed May 14, 1964, Ser. No. 367,386 Claims priority, application Great Britain, May 16, 1963, 19,483/ 63 3 Claims. (Cl. 219--421) This invention relates to furnaces and provides an electrically heated furnace, of relatively large capacity for its overall size, suitable for melting metal and holding molten metal ready for use, such as in diecasting.

According to the invention, an electrically heated furnace comprises a thermally insulate-d bath with one or more electrical immersion heaters inserted through a wall of the bath and extending downwardly inclined through a major part of the depth of the bath.

Preferably, the bath is of oblong shape in plan and each heater is inserted through one of the longer side walls thereof so as to extend across a substantial part of the width of the bath.

This arrangement enables the furnace to have substantially the same overall dimensions as a simple insulated bath of the same capacity, there being no external combustion or electrical induction heating apparatus as in existing metal melting and holding furnaces, the top of the furnace is unimpeded, so that it can be utilised efiiciently for charging and removing metal, and the area of heating has a substantial extent both in depth and across the bath.

In a preferred construction, the bottom of the bath slopes upwardly to the side closely beneath and at the same angle as the inclined immersion heaters and, as a further feature, the immersion heaters are protected, against impact by metal charged into the bath, by inclined ribs or partitions upstanding from the bottom of the bath and projecting between and slightly above the individual immersion heaters.

Each immersion heater has a protective tubular sheath which is close-d at its lower end and is supported by its upper, open, end which extends through and is sealed into the side wall of the bath and its thermal insulation. The sheath may be made of a suitable refractory material such as silicon carbide or of a suitable ferrous metallic material.

Preferably, the heating element of each heater is a resistor of a refractory material, such as silicon carbide, in the form of a tube, or rod, inserted axially in the respective sheath, through the upper end thereof, to rest on an insulating and central locating support in the bottom of the sheath so that the wall of the sheath has a clearance around the element. The upper end of the element has a supporting collar or bush in the upper end of the sheath and is provided with electrical connections and terminals for connection to an electrical power supply. This construction enables the heating elements to be withdrawn from their sheaths, for servicing or replacement, without disturbing the construction of the furnace bath itself.

Any other immersion heater may however be used, for example the known kind of heater in which the element is of resistance Wire wound on a former and enclosed in a sheath.

The top of the furnace bath is provided with thermally insulated hinged or removable covers for access openings for charging the bath with metal and removing molten metal therefrom.

A preferred construction of a furnace in accordance ree with the invention isillustrated on the accompanying drawing.

The drawing shows a cross-section of a furnace which is of rectangular shape in plan and can be of any length, to suit requirements, the parts shown by the drawing being duplicated as many times as necessary along the length of the furnace to suit the capacity of the furnace.

The furnace as shown consists of a bath 1 which may be made of cast iron for holding relatively low melting point metals, such as zinc, or of a ceramic material, for example, for holding molten metal at high temperatures.

The bath 1 is mounted within a casing 2 packed with thermal insulating material 3, such as vermiculite.

The top of the bath is partly closed by an insulated cover 4 and a hinged lid 5, for charging the bath with metal, an opening 6 being left for the insertion of ladles for removing molten metal.

At one side, the bottom of the bath slopes upwardly and has, spaced along the bath, upstanding partitions 7 with upper edges similarly sloped.

Between adjacent partitions 7 an inclined tubular sheath 8, of silicon carbide for example, is mounted by its upper end which extends through the side wall of the bath 1 and its casing 2 and is sealed in a sleeve bracket 9.

In the sheath 8, an electrical resistance heating element 10 is removably mounted. The element shown is a helically slotted tube of a refractory electrical resistance material, such as silicon carbide, which rests by its lower end on a locating and insulating plug 11 in the closed lower end of the sheath 8 and is supported in the upper end of the sheath 8 by an insulating bush 12.

Electrical connections 13 are joined to the upper end of the element 10 and are enclosed by a protective cover 14 which closes the upper end of the sheath 8.

It can be seen from the drawing that the immersion heater, consisting of the element 10 in its sheath 8, extends through a substantial part of the depth and width of the bath 1 and thus can efficiently melt or maintain metal molten in the bath. The partitions 7 protect the heater from damage by metal ingots charged into the bath through the filling opening, when the lid 5 is raised, or by ladies inserted through the opening 6.

We claim:

1. An electrically heated furnace for molten metal comprising a thermally insulated bath, said bath being of oblong shape in plane and having longer side walls and shorter end walls and a bottom at the lower edges of the walls, and at least one electrical immersion heater inserted through one of the longer side walls and extending within the bath in a downwardly inclined direction through a major part of the depth of the bath and across a substantial part of the width of the bath, said bath bottom having a part which slopes upwardly to said one of the longer side walls, said part of the bath bottom lying closely beneath the said heater and at substantially the same angle as the inclination of the heater, said bath further having on each side of each said heater a partitron upstanding from the sloping part of the bottomand extending above the said heater.

2. A furnace according to claim 1, in which the upper edges of said partitions are slightly above and are inclined at substantially the same angle as the inclination of the heater.

3. A furnace according to claim 1, in which each heater has a protective tubular sheath, said sheath is closed at its lower end and is supported in the wall of the bath by the upper end of said sheath which extends through and is sealed into said wall of the bath, and a heater element is mounted in said sheath and is withdrawable through the upper end of said sheath.

(References on following page) References Cited by the Examiner UNITED STATES PATENTS Smith 219-436 Millner 2'19421 Woodson 219421 X Churchill 21943'7 X Franz 219-421 2,536,747 1/1951 Hynes 219315 2,720,686 10/ 1955 Higgins et a1. 2279 X FOREIGN PATENTS 156,562 5/ 1954 Australia. 406,567 3/1934 Great Britain. 294,613 2/ 1954 Switzerland.

ANTHONY BARTIS, Primary Examiner. 

1. AN ELECTRICALLY HEATED FURNACE FOR MOLTEN METAL COMPRISING A THERMALLY INSULATED BATH, SAID BATH BEING OF OBLONG SHAPE IN PLANE AND HAVING LONGER SIDE WALLS AND SHORTER END WALLS AND A BOTTOM AT THE LOWER EDGES OF THE WALLS, AND AT LEAST ONE ELECTRICAL IMMERSION HEATER INSERTED THROUGH ONE OF THE LONGER SIDE WALLS AND EXTENDING WITHIN THE BATH IN A DOWNWARDLY INCLINED DIRECTION THROUGH A MAJOR PART OF THE DEPTH OF THE BATH AND ACROSS A SUBSTANTIAL PART OF THE WIDTH OF THE BATH, SAID BATH BOTTOM HAVING A PART WHICH SLOPES UPWARDLY TO SAID ONE 